Metal-TUD-1 catalyzed aerobic oxidation of cyclohexane: A comparative study

Article abstract of DOI:10.1071/CH08471

The relative performance of various metal-incorporated mesoporous silicas of the TUD-1 structure type (M-TUD-1, where M ≤ Ti, Cr, Co, Fe, Cu, Mn) in the selective aerobic oxidation of cyclohexane with tert-butylhydroperoxide and cyclohexylhydroperoxide (CHHP) to the respective hydroperoxides and subsequent decomposition to the alcohol and ketone is reported. In particular, relationships regarding metal type and loading, silica structure type and peroxide initiator are elucidated, to show that it is possible to tune catalysts for either CHHP formation or CHHP decomposition.

Full text of DOI:10.1071/CH08471

Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2009, 62, 360–365
www.publish.csiro.au/journals/ajc
Metal-TUD-1 Catalyzed Aerobic Oxidation of Cyclohexane:
∗
A Comparative Study
Ramanathan Anand,A,B,C Mohamed S. Hamdy,
A,D
Rudy Parton,E
A,F,H
A
B,G
Thomas Maschmeyer,
Jacobus C. Jansen, Roger Gläser,
A
A,H
Freek Kapteijn, and Ulf Hanefeld
AGebouw voor Scheikunde, Technische Universiteit Delft, Julianalaan 136,
2
628 BL Delft, The Netherlands.
B
C
Institute of Chemical Technology, University of Stuttgart, 70550 Stuttgart, Germany.
Present address: Department of Chemistry, University College of Engineering,
Tindivanam (Anna University, Chennai), Saram 604307, Tamil Nadu, India.
D
Present address: Valorisation of Plant Production Chains, Wageningen University,
PO Box 17, 6700 AA Wageningen, The Netherlands.
E
DSM Research, 6160 MD Geleen, The Netherlands.
F
Present address: School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.
G
Present address: Institute of Chemical Technology, University of Leipzig, Linnéstr. 3,
4103 Leipzig, Germany.
Corresponding authors. Email: u.hanefeld@tudelft.nl; th.maschmeyer@chem.usyd.edu.au
0
H
The relative performance of various metal-incorporated mesoporous silicas of the TUD-1 structure type (M-TUD-1,
where M =Ti, Cr, Co, Fe, Cu, Mn) in the selective aerobic oxidation of cyclohexane with tert-butylhydroperoxide and
cyclohexylhydroperoxide (CHHP) to the respective hydroperoxides and subsequent decomposition to the alcohol and
ketone is reported. In particular, relationships regarding metal type and loading, silica structure type and peroxide initiator
are elucidated, to show that it is possible to tune catalysts for either CHHP formation or CHHP decomposition.
Manuscript received: 31 October 2008.
Final version: 23 February 2009.
Introduction
O
H
O
O
H
The selective oxidation of cyclohexane is of great industrial
importance and at the same time it forms a major academic
challenge. The reaction is commonly kept at low conversions
CHHP
Undesired
overoxidation
products
O2
[
1]
(
∼5%), as all the desired mono-oxygenated products are more
[2–9]
A
K
reactive than the starting material (Scheme 1).
Hence, the
O
first challenge is to find catalysts that accelerate the selec-
tive oxygenation of cyclohexane to cyclohexylhydroperoxide
(
CHHP), cyclohexanol (A), and cyclohexanone (K). CHHP is
very reactive and could be a source of undesired overoxidation
products. Thus, the second challenge is to selectively decom-
pose CHHP into A and K. All this should be achieved while
not promoting A and K oxidation, because this mixture (also
known as KA-oil) is the desired product. Industrially the reac-
tion is performed by liquid-phase air oxidation of cyclohexane at
Desired products
Scheme 1. Aerobic oxidation of cyclohexane is unselective. Overoxidation
is a major problem.
straightforward recycling, a target often not achieved in the
◦
[1]
[10,11]
1
40–180 C at 0.8–2 MPa. It is either performed in a two-step
current processes.
approach, an uncatalyzed aerobic formation of CHHP followed
by catalytic decomposition to A and K, or in a one-pot pro-
cess with catalytic CHHP formation and decomposition. In both
cases conversions need to be kept low to achieve a selectivity
of above 90% for the mono-oxygenated products. It is, there-
fore, highly desirable to develop catalysts with higher selectivity.
In addition, these catalysts should be heterogeneous to ensure
Recently, we have described the incorporation of metals into
the mesoporous, three-dimensional, sponge-like silica TUD-1.
These materials are ideally suited for heterogeneous catalysis
as they show virtually no diffusion limitation associated with
the pore network, are very stable, and can be recycled many
times. The syntheses of M-TUD-1s are highly reproducible and
yield well-defined materials. At Si/M ratios of 25 and higher
∗
Dedicated to Joop Peters on the occasion of his 65th birthday.
©
CSIRO 2009
10.1071/CH08471
0004-9425/09/040360

Aerobic Oxidation of Cyclohexane
361
Table 1. Physico-chemical properties of M-TUD-1
SBETB [m g
2
−1
]
VmesoC [cm g
3
−1
]
DmesoD [nm]
Isolated M
+n
Nanoparticles
M-oxide
Bulk M-oxide
M-TUD-1
Si/M ratio
after calcination)A
(
Co-TUD-1
Ti-TUD-1
100 (108)
1.7 (1.4)
619
516
570
741
764
633
555
628
565
568
626
630
778
818
0.73
0.28
0.36
0.5
0.78
0.99
1.37
1.1
1.54
1.82
0.65
0.95
0.99
0.95
4
++
++
++
++
++
++
++
++
++
++
+
−
+
+
+
+
+
+
−
−
−
+
+
+
−
−
−
0.2
3.5
3.6
3.7
7.2
13.4
9.1
8.4
15.9
4.6
8.8
6.8
5.8
2
5
.5 (2.3)
(4.6)
−
−
1
2
4
0 (9.7)
0 (23.8)
0 (38.8)
−
−
−
100 (112)
−
Cr-TUD-1
Fe-TUD-1
Mn-TUD-1
100 (130)
100 (113)
10 (8)
−
−
++
+
2
5
5 (22)
0 (45)
+
++
++
−
100 (89)
−
A
Based on elemental analysis.
Specific surface area.
Mesopore volume.
Mesopore diameter: (++) abundantly present, (+) weakly or poorly present, (−) absent.
B
C
D
Table 2. Aerobic oxidation of cyclohexane over M-TUD-1 (Si/M = 100) in the presence of TBHP as radical initiator
M-TUD-1
Conv.A [mol%]
KB [mol%]
AC [mol%]
CHHP [mol%]
SmonoD [mol%]
K/A
Ti
Cr
2.9
3.2
3.7
2.7
2.6
2.9
1.3
33.4
48.2
35.4
37.8
42.1
26.6
29.5
55.5
19.9
50.4
49.8
42.8
52.3
25.8
1.2
6.6
3.5
1.6
1.4
3.4
6.5
90.5
78.3
90.9
91.6
88.8
85.5
67.7
0.6
2.4
0.7
0.8
1.0
0.5
1.1
Co
Fe
Cu
Mn
Blank
A
Conversion.
Ketone.
B
C
Alcohol.
D
Selectivity to mono-oxygenated products; Conditions: Cyclohexane 175 mmol, TBHP 0.05 mmol, PhCl 1 g (internal
◦
standard), T 120 C, Catalyst 0.1 mmol of active metal species, for details see Experimental.
the metal is incorporated as an isolated species, which ensures
excellent accessibility and activity. M-TUD-1s (where M =Ti,
Cr, Co, Fe, Cu, Mn) have proven their value as catalysts in var-
ious different reactions and, in particular, in the oxidation of
cyclohexane with tert-butylhydroperoxide (TBHP) as sacrificial
The elemental analysis by inductively couple plasma optical
emission spectroscopy (ICP-OES) and porosity measurements
obtained from N2 sorption studies at 77 K are listed in Table 1.
Elemental analysis indicated that the Si/M ratios in the calcined
samples were the same as those in the initial synthesis gel. N2
sorption studies of these materials show a type-IV isotherm, as
indicated by the large uptake of nitrogen at relative pressures
between p/p0 = 0.5 and 0.9 as a result of capillary condensation
in the mesopores. The absence of large mesopores, macropores,
or surface roughness in the measurable range (20 to ∼500 nm)
is visible as the adsorption/desorption isotherms also show a
plateau at relative pressures above p/p0 = 0.8–0.9. In general,
a higher loading of metal leads to a decrease in pore size and
specific surface area, and the presence of some percolation or
networking effects can also be deduced from a non-parallel
adsorption and desorption isotherm.
[
12–22]
oxidant.
Based on these positive results we here describe
the M-TUD-1 catalyzed oxidation of cyclohexane by molecular
oxygen, initiated either by TBHP or CHHP.
Results and Discussion
All M-TUD-1 were prepared and characterized as described
[
12–22]
earlier.
The X-Ray powder diffraction (XRD) patterns of
◦
all M-TUD-1 showed a reflection around 2θ = 0.5–2.0 and,
thus, demonstrated a meso-structured character. In general, a
higher loading of metal leads to a decrease in the intensity of this
reflection. In addition, nanoparticles of M oxides are commonly
noted at Si/M ratios of less than 25. The mesoporous nature
of all these materials was further confirmed by high-resolution
transmission electron microscopy (HR-TEM) studies. In these
studies the nanoparticles of M-oxide formed at higher loading
became visible.
M-TUD-1s with Si/M ratios of 100 were utilized in the aero-
bic cyclohexane oxidation. The framework-incorporated, and
thus isolated, metals were Ti, Cr, Co, Fe, Cu, and Mn. The reac-
◦
tions were performed at 120 C in an autoclave and initiated
with TBHP (Table 2). The highest conversions were observed
with Co-TUD-1, which also gave the best selectivity towards

3
62
R. Anand et al.
Table 3. Aerobic oxidation of cyclohexane M-TUD-1 (Si/M = 100) in the presence of CHHP as radical initiator
M-TUD-1
Conv.A [mol%]
KB [mol%]
AC [mol%]
CHHP [mol%]
SmonoD [mol%]
K/A
Ti
Cr
0.5
3.6
3.8
1.6
2.2
3.1
0.6
24.9
64.5
30.8
53.1
43.5
21.2
4 9.3
43.0
8.3
12.7
0.2
0.5
3.6
2.2
2.3
3.2
91.5
75.7
90.4
90.0
82.9
61.8
93.0
0.6
7.7
0.5
1.8
1.3
0.6
1.2
Co
Fe
Cu
Mn
Blank
56.5
29.4
34.5
36.2
39.0
A
Conversion.
Ketone.
B
C
Alcohol.
D
Selectivity to mono-oxygenated products; Conditions: Cyclohexane 175 mmol, CHHP 0.05 mmol, PhCl 1 g (internal
◦
standard), T 120 C, Catalyst 0.1 mmol of active metal species, for details see Experimental.
Table 4. High-throughput CHHP decomposition studies over Co- and Ti-TUD-1
Catalyst
Si/M
mg
CHHP
AA
[mol%]
KB
[mol%]
Acids
[mol%]
Esters
[mol%]
Other
[mol%]
SmonoC
[mol%]
Conv.D
[mol%]
[mol%]
Co-TUD-1
Ti-TUD-1
100
1.7
10.1
10.2
10.6
10.1
10
9.9
9.9
10
0.3
81.3
82.0
81.3
77.2
74.5
71.5
71.8
82.9
84.55
61.5
10.6
10.7
11.0
13.3
15.3
17.2
17.4
9.4
35.1
6.4
5.7
6.2
7.9
8.4
9.4
8.8
5.7
4.16
2.4
0.9
0.8
0.7
0.7
0.9
0.9
1.2
1.1
0.94
0.0
0.0
0.0
0.0
0.0
0.1
0.1
0.1
0.0
0.35
0.7
0.8
0.8
0.8
0.8
0.8
0.9
0.8
0.9
0.86
96.9
98.3
98.3
98.5
98.4
98.2
98.1
98.0
98.0
99.7
3.9
3.0
3.9
8.7
11.9
15.4
15.1
2.0
2.5
5
0
0
0
1
2
4
100
Blank
Initial feed
composition
—
9.14
A
Alcohol.
Ketone.
B
C
◦
Selectivity to mono-oxygenated products; Conditions: T 70 C, P 5.5 bar N2, stirring rate 300 rpm, t 90 min, for details see Experimental.
Conversion.
D
mono-oxygenated products. Cr-TUD-1 was also very active but
To understand the factors that determine the activity of Ti
incorporated into TUD-1, Ti-TUD-1 catalysts with different
Si/Ti ratios were prepared. In CHHP decomposition studies
they were compared directly with the most active catalyst in
the CHHP-induced aerobic cyclohexane oxidation, Co-TUD-1
(Table 4). As expected, Co-TUD-1 converted almost all CHHP,
displaying high selectivity for mono-oxygenated products. All
Ti-TUD-1 samples exhibited high selectivity. However, this was
because of their very low activity. A clear trend can be observed.
With increasing Ti loading the activity of the Ti-TUD-1 drops.
Thus the already weak catalysts Ti-TUD-1 with Si/Ti = 100 and
40 exhibit approx. 15% conversion. In these catalysts the Ti is
framework incorporated and isolated. With the increase of Ti
in Ti-TUD-1 the amount of Ti–O–Ti clusters increases, TiO2
being present at higher concentrations. This leads to a drop of
the already low activity. Hence, it can be concluded that iso-
latedTi inTi-TUD-1 exhibits relatively better activity for CHHP
decomposition. These results are in contrast to that expected
as hydrogen peroxide decomposition is accelerated by the pres-
ence of titania clusters, whereas isolated sites form relatively
stable complexes in the absence of oxidizable species such as
alkenes.[
displayed low selectivity. Ti-TUD-1 and Mn-TUD-1 showed
similar activity, with poor selectivity in the case of Mn-TUD-1.
Fe-TUD-1 and Cu-TUD-1 were only moderately active and thus
displayed a rather high selectivity after the same reaction time,
Fe-TUD-1 being somewhat more selective.
When TBHP was replaced with CHHP, the initiator com-
monly employed in industry, the picture changed completely
(
Table 3). Ti-TUD-1 lost all its activity, in line with the ear-
lier described inability of Ti to catalyze the decomposition
[
23,24]
of CHHP.
Fe-TUD-1 and Cu-TUD-1 now displayed low
activity, in the case of Cu-TUD-1 coupled with low selectivity.
Co-TUD-1, Cr-TUD-1, andMn-TUD-1werethemostactivecat-
alysts. In addition, Co-TUD-1 exhibits a very high selectivity,
making it the catalyst of choice in this row. Extensive studies of
Co-TUD-1 with different Si/Co ratios confirmed that Co-TUD-1
with Si/Co = 100 is a very stable, active, and selective cata-
lyst for the aerobic cyclohexane oxidation.[
12,13,25]
Mn-TUD-1,
however, combines high activity with very low selectivity.
In order to gain a better understanding of the factors that
decrease the activity of a catalyst or its selectivity, Ti-TUD-1
and Mn-TUD-1 were investigated more closely. Based on this
the active and selective catalysts might be improved even
further.
26]
The above results also highlight the special position of the
higher catalytic activity of Ti-TUD-1 when TBHP is used as a

Aerobic Oxidation of Cyclohexane
363
Table 5. Aerobic oxidation of cyclohexane over various Ti-TUD-1s in the presence of TBHP as radical initiator
Catalyst
Si/Ti
Conv.A [mol%]
KB [mol%]
AC [mol%]
SmonoD [mol%]
K/A
Blank
—
100
50
20
10
2.4
2.8
2.4
3.4
3.7
34
42.8
55.5
38.6
33.7
23.7
79.2
90.5
87.2
85.6
81.2
0.8
0.6
1.1
1.4
2.4
Ti-TUD-1
Ti-TUD-1
Ti-TUD-1
Ti-TUD-1
33.4
42.4
48.5
54.9
A
Conversion.
Ketone.
B
C
Alcohol.
D
Selectivity to mono-oxygenated products; Conditions: Cyclohexane 175 mmol, TBHP 0.05 mmol, PhCl 1 g (internal
◦
standard), T 120 C, Catalyst 0.1 mmol of active metal species, for details see Experimental.
radical initiator in the aerobic cyclohexane oxidation. To gain
more insight into this extraordinary difference, Ti-TUD-1s with
different Si/Ti ratios were studied for their activity in this reac-
tion (Table 5). An increase in Ti loading leads to formation
of nanoparticles of TiO2 above 2.5 mol% of Ti in TUD-1 (see
Table 1). As the catalytic activity per mole of Ti increases with
the Ti loading of the Ti-TUD-1 catalysts (0.1 mmol of active
metal used in each experiment), this strongly indicates that the
nanoparticles of TiO2 are the active species in this aerobic oxi-
dation of cyclohexane, whereas these catalysts are not active in
the decomposition of CHHP (Table 4). Therefore, the conver-
sion of cyclohexane with these catalysts was only around 0.5%
when CHHP was used as initiator (Table 3). These observations
are consistent with the conclusion that Ti-TUD-1, in particular
whencontainingTiO2 nanoparticles, isspecificforthedecompo-
sition ofTBHP and thus theTHBP-initiated aerobic cyclohexane
oxidation.
Table 6. Aerobic oxidation of cyclohexane over various manganese
based catalysts in the presence of CHHP as radical initiator
Catalyst
Si/Mn
Conv. [%]
K
A
SmonoA
K/A
Blank
—
100
50
25
10
2.4
3.1
2.2
2.1
4.0
2.1
2.4
34.0
21.2
21.1
24.2
23.3
26.6
28.2
42.8
36.2
41.9
47.9
49.9
52.3
51.0
79.2
61.8
65.3
74.7
78.6
85.5
84.3
0.8
0.6
0.5
0.5
0.5
0.5
0.6
Mn-TUD-1
Mn-TUD-1
Mn-TUD-1
Mn-TUD-1
Mn-MCM-48
Mn-MCM-41
50
50
A
Selectivity to mono-oxygenated products; Conditions: Cyclohexane
◦
175 mmol, CHHP0.05 mmol, PhCl1 g(internalstandard),T 120 C, Catalyst
0.1 mmol of active metal species, for details see Experimental.
To increase our understanding of the high activity of
Mn-TUD-1 in combination with its low selectivity, a series of
Mn-TUD-1s with different Si/Mn ratios were prepared. To allow
comparison, Mn-MCM-48 and Mn-MCM-41 were also consid-
ered (Table 6). With an increase in the amount of Mn in TUD-1,
a slight decrease in conversion of cyclohexane combined with
an increase in selectivity for mono-oxygenated products can be
observed. Surprisingly, Mn-TUD-1 with a Si/Mn ratio of 10 then
showed a high conversion of 4% while maintaining selectivity
Conclusions
Out of all the M-TUD-1 catalysts screened, Co-TUD-1 dis-
plays the highest activity combined with the highest selectivity.
Ti-TUD-1 is a catalyst with excellent selectivity but induces
only little conversion of CHHP. The performance is linked to
the Ti loading: low loading yields Ti-TUD-1 with isolated Ti
species and ensures the highest observed activity for this metal in
CHHP decomposition. HighTi loading leads to extra-framework
titanium dioxide particles that are effectively inactive towards
CHHP decomposition. In contrast, they are very active in the
decomposition ofTBHP. In the case of the active, but unselective,
Mn-TUD-1, higher Mn loadings significantly improve selectiv-
ity without loss of activity. Manganese oxide clusters at high Mn
of around 80% for mono-oxygenated products.
From previous electron paramagnetic resonance studies,[21]
it was concluded that a higher manganese content in the
2
+
Mn-TUD-1 molecular sieve leads to a lower fraction of Mn
species. Consequently more Mn3 sites are present. Part of
+
the latter fraction comprises an extra-framework phase, that
is, Mn2O3. This bulk Mn oxide seems to be responsible for
the higher activity whereas Mn in the isolated tetrahedrally
incorporated sites seems to predominantly oxidize the initially
produced mono-oxygenated products K and A, thus having a
detrimental effect on the selectivity of the catalyst. The results
are comparable with those of the well-known mesoporous mate-
rials Mn-MCM-41 and Mn-MCM-48 (Table 6). However, these
catalysts exhibit a higher selectivity for the mono-oxygenated
products, which may be due to the texture, as they are ordered
loading contain more Mn3 , which improve selectivity. Com-
paring all results it is evident that both metal and Si/M ratio are
important parameters for the activity of the M-TUD-1 catalysts
in the aerobic cyclohexane oxidation. In particular, whether the
metal is completely incorporated into the silica framework or is
present as metal oxide clusters can greatly influence the activity
and selectivity of the catalyst. Consequently, the relative fraction
of framework-incorporated and extra-framework metal sites may
offer a tool to improve the activity and direct the selectivity of
M-TUD-1 catalysts for selective oxidation reactions.
+
[27]
mesoporous silicas, whereas TUD-1 is amorphous. Liu et al.
studied three types of metal-containing molecular sieves with
AFI, AEL, and CHA structures and concluded that both metal
types and structure of molecular sieves influenced activity
and selectivity. However, more ordered structures might not
automatically lead to higher selectivity.
Experimental
Materials and Methods
All M-TUD-1s were prepared as described earlier.[12–22]

3
64
R. Anand et al.
Synthesis of Co-TUD-1[
12]
carried out on anAgilent 6890 gas chromatograph equipped with
a split inlet (200 C, split ratio 10.0), a Sil 5 CB capillary column
◦
A clear synthesis mixture with a molar ratio composition of
SiO2/0.01 CoO/0.5 tetraethylammonium hydroxide (TEAOH)/
triethanolamine (TEA)/11 H2O was prepared by adding a
solution of 0.23 g of CoSO4·7H2O (Aldrich) in 5 mL of deion-
ized water to 17.4 g of tetraethyl orthosilicate (TEOS, +98%,
ACROS) and stirring for a few minutes. Subsequently, a mixture
of 12.6 g of TEA (97%, ACROS) with 5 mL of deionized water
was added dropwise before finally adding 10.3 g of TEAOH
−
1
(
50 m × 0.53 mm; constant flow of carrier gas N2 4.0 mL min
;
◦
temperatureprogram:isothermalat45 Cfor35 min, followedby
heating to 200 C with a rate of 15 C min , and subsequently to
00 Cwitharateof20 C min , finaltime10 minat300 C)and
1
◦
◦
−1
◦
◦
−1
◦
3
◦
a FID detector (set to 325 C). The concentration of carboxylic
acid side-products was determined by GC analysis from a sepa-
rate sample after conversion into the respective methyl esters –
an extensive description of the analyses is given in reference.[
In addition, we are grateful to the analytical department of DMS
for confirming all our analytical data.
28]
(
35%, Aldrich). The mixture was aged at room temperature for
◦ ◦
4 h, dried at 100 C for 24 h, and calcined at 600 C for 10 h at
2
◦
−1
a rate of 1 C min in the presence of air.
The term Smono as used here refers to the selectivity for mono-
oxygenated products.
Synthesis of Ti-TUD-1
Ti-TUD-1 was prepared according to literature methods.[17]
Material Characterization
Synthesis of Cu-TUD-1[
14]
Chemical analyses of M-TUD-1 were performed by dissolv-
ing the samples in 1% HF and 1.3% H2SO4 solution (wt.-%)
and measuring them with ICP-OES on a Perkin–Elmer Optima
A mixture of 24.7 g of TEA (97%, ACROS) and 6.5 g of deion-
ized water was added dropwise into a mixture of 33.2 g of
TEOS (98%, ACROS) and a copper salt solution (0.38 g of
Cu(NO3)2·3H2O in 3 mL of deionized water) while stirring.
Once the addition was complete, the solution was stirred for
a few minutes followed by addition of 33.2 g of TEAOH (35%,
Aldrich). The mixture was then aged at room temperature for
4 h, dried at 98 C for 24 h, followed by a hydrothermal treat-
ment at 180 C for 8 h. Finally the solid products were calcined
at 600 C for 10 h with a ramp rate of 1 C min
3000DV instrument. Powder XRD patterns were obtained on
a Philips PW 1840 diffractometer equipped with a graphite
monochromator using CuKα radiation. The textural parameters
were evaluated from volumetric nitrogen physisorption at 77 K.
Before the physisorption experiment the samples were dried
under vacuum at 623 K for 16 h and the nitrogen adsorption
and desorption isotherms were measured on a Quantachrome
Autosorb-6B at 77 K. TEM was performed using a Philips
CM30T electron microscope with a LaB6 filament as the source
of electrons operated at 300 kV. UV-vis spectra were collected at
room temperature on a Shimadzu UV-2450 spectrophotometer
using BaSO4 as reference. The physico-chemical properties of
M-TUD-1 are shown in Table 1.
◦
2
◦
◦
◦
−1
.
Synthesis of Fe-TUD-1[
19]
A mixture of 24 g of TEA (97%, ACROS) with 4.5 mL of de-
ionized water was added dropwise into a mixture of 33.2 g of
TEOS (+98%, ACROS) and ferric chloride (Aldrich) solution
(
0.25 g and 5 mL of de-ionized H2O) while stirring vigorously.
Aerobic Oxidation of Cyclohexane
After stirring for ∼30 min, 32.9 g ofTEAOH (35%,Aldrich) was
added.The mixture was aged at room temperature for 24 h, dried
All cyclohexane oxidation experiments were carried out in a
100 mL semi-batch, mechanically stirred Parr autoclave (series
4560, Hastalloy C), equipped with a pressure gauge (range 0–
40 bar). The autoclave was charged with 20 mL of a mixture of
cyclohexane (14.77 g, 175 mmol) and chlorobenzene (1 g, inter-
nal GC standard) and a trace (0.05 mmol) of CHHP or TBHP as
radical initiator. M-TUD-1 catalyst (0.1 mmol of M) was added
directly to the reaction mixture. The autoclave was sealed, pres-
surized to 15 bar with a mixture of N2 and O2 (8 vol-%) gas,
◦
at ∼100 C for 24 h, and then hydrothermally treated in aTeflon-
◦
lined stainless steel autoclave at 180 C for 8 h. Finally the solid,
◦
as-synthesized samples were calcined at 600 C for 10 h using a
ramp rate of 1 C min in air.
◦
−1
Synthesis of Cr-TUD-1[
20]
Cr-TUD-1 was synthesized by aging, drying, and calcination of
a homogeneous synthesis mixture. The latter consists of a solu-
tion of Cr(NO3)3·9H2O, a silicon alkoxide source (TEOS), and
TEA. An aqueous chromium salt solution (0.38 g of chromium
nitrate and 2 mL of H2O) was added dropwise into TEOS
◦
and then rapidly heated to 120 C and held at that temperature
for a period of 24 h. The autoclave was then cooled to room
◦
temperature by a jet of air and subsequently to 5 C by immer-
sion in an ice bath. After release of the excess pressure, acetone
(
19.91 g, +98%, ACROS). While stirring, a mixture of 14.4 g of
(20 mL) was added by a port of the autoclave head for desorbing
TEA (97%, ACROS) and 3.6 mL of H2O was added dropwise.
Finally, 19.7 g ofTEAOH (35%,Aldrich) was added, again drop-
wise. After stirring for 2 h, a clear and pale green solution was
obtained, with a molar ratio composition of SiO2/0.01Cr2O3/
polar reaction products from the catalyst surface. The mixture
was stirred for an additional 15 min before samples were taken
for GC analysis. The cited conversions were calculated by refer-
ring the sum of the determined concentrations of all identified
cyclohexane-derived products to the initial cyclohexane concen-
tration in the respective catalytic experiments. All conversions
are reported in the tables as mol percentages. The blank experi-
ments do not contain any catalyst. In terms of reaction conditions
and in all other respects they have been treated the same as those
that contain a M-TUD-1 catalyst.
0
.5 TEAOH/1TEA/11 H2O. The mixture was aged at room tem-
◦
perature for 24 h, dried at 100 C for 24 h, hydrothermally treated
in a stainless steel Teflon-lined autoclave, and then calcined at
◦ ◦ −1
00 C for 10 h using a heating ramp rate of 1 C min in air.
6
Synthesis of Mn-TUD-1
Mn-TUD-1 was prepared according to literature methods.[21]
The calcined M-TUD-1 (M =Ti, Cr, Co, Fe, Cu, Mn) cat-
◦
CHHP Decomposition
alysts were activated in a static air oven at 180 C overnight
before their use in the catalytic experiments. Gas chromato-
graphy (GC) analysis of cyclohexane oxidation products was
High throughput experimentation (HTE) was utilized to study
the M-TUD-1 catalyzed decomposition of CHHP. The HTE runs

Aerobic Oxidation of Cyclohexane
365
were performed using a custom-made 96-fold parallel reactor
[9] I. Hermans, J. Peeters, P. A. Jacobs, Top. Catal. 2008, 48, 41.
doi:10.1007/S11244-008-9051-X
10] R. A. Sheldon, M. Wallau, I. W. C. E. Arends, U. Schuchardt, Acc.
Chem. Res. 1998, 31, 485. doi:10.1021/AR9700163
(
1
A96 reactor), which holds 96 × 5 mL glass reaction vials.About
[
[
[
[
0 mg of M-TUD-1 catalyst was added to the reaction vials
and subsequently filled with 1 mL of a solution of CHHP in
cyclohexanewithbiphenylasinternalstandard(excludingcyclo-
hexane, the feed contained 84.55 mol% of CHHP, cyclohexanol
11] R.A. Sheldon, I.Arends, U. Hanefeld, Green Chemistry and Catalysis
2
007 (Wiley-VCH: Weinheim).
12] R. Anand, M. S. Hamdy, U. Hanefeld, T. Maschmeyer, Catal. Lett.
004, 95, 113. doi:10.1023/B:CATL.0000027283.70453.1A
9
0
.14 mol%, cyclohexanone 4.16 mol%, acids 0.94 mol%, esters
.35 mol%, and others 0.86 mol%). The reaction vials were then
2
13] M. S. Hamdy, A. Ramanathan, T. Maschmeyer, U. Hanefeld, J. C.
transferred to theA96 reactor, closed, and flushed for 5 min with
nitrogen and pressurized up to 5.5 bar nitrogen pressure. In paral-
lel with these manipulations the temperature was increased up to
Jansen, Chem. Eur. J. 2006, 12, 1782. doi:10.1002/CHEM.200500166
[14] M. S. Hamdy, G. Mul, W. Wei, R. Anand, U. Hanefeld, J. C. Jansen,
J. A. Moulijn, Catal. Today 2005, 110, 264. doi:10.1016/J.CATTOD.
2005.09.026
[15] R.Anand, M. S. Hamdy, P. Gkourgkoulas,T. Maschmeyer, J. C. Jansen,
U. Hanefeld, Catal. Today 2006, 117, 279. doi:10.1016/J.CATTOD.
◦
◦
7
7
0 C. The set point was 75 C for the oil bath to give the desired
0 C in the reactor. The stirring rate was set at 300 rpm. The
◦
reaction was left for 90 min at the reaction temperature and then
the reactor was allowed to cool by itself. When the temperature
2006.05.031
[
16] Z. Shan, E. Gianotti, J. C. Jansen, J. A. Peters, L. Marchese,
◦
was below 28 C, the pressure in the system was released slowly
T. Maschmeyer, Chem. Eur. J. 2001, 7, 1437. doi:10.1002/1521-
over a period of 5 min. The analysis was performed as described
above.
3765(20010401)7:7<1437::AID-CHEM1437>3.0.CO;2-M
[
17] Z. Shan, J. C. Jansen, L. Marchese, T. Maschmeyer, Micropor.
Mesopor. Mater. 2001, 48, 181. doi:10.1016/S1387-1811(01)00342-0
Acknowledgements
[18] M. S. Hamdy, O. Berg, J. C. Jansen, T. Maschmeyer, J. A. Moulijn,
G. Mul, Chem. Eur. J. 2006, 12, 620. doi:10.1002/CHEM.200500649
Generous financial support for this work from the European Commis-
sion through the Network of Excellence ‘INSIDE-POReS’ (contract no.
NMP3-CT-2004–500895) is gratefully acknowledged. Part of this work was
performed within the Collaborative Research Centre SFB 706 (Selective
Catalytic Oxidations Using Molecular Oxygen; Stuttgart), funded by the
German Research Foundation. The authors thank the analytical department
at DSM Research in Geleen for confirming our analysis results.
[
[
19] M. S. Hamdy, G. Mul, J. C. Jansen, A. Ebaid, Z. Shan, A. R. Overweg,
T. Maschmeyer, Catal.Today 2005, 100, 255. doi:10.1016/J.CATTOD.
2004.10.018
20] M. S. Hamdy, O. Berg, J. C. Jansen, T. Maschmeyer, A. Arafat,
J. A. Moulijn, G. Mul, Catal. Today 2006, 117, 337. doi:10.1016/
J.CATTOD.2006.05.058
[
21] A. Ramanathan, T. Archipov, R. Maheswari, U. Hanefeld, E. Roduner,
R. Gläser, J. Phys. Chem. C 2008, 112, 7468. doi:10.1021/JP0739216
22] M. S. Hamdy, Ph.D. Thesis, Technische Universiteit Delft, Delft, The
Netherlands, 2005, open access on: http://www.library.tudelft.nl/ws/
search/publications/index.htm.
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